Method for producing quinacridone solid solution pigment, pigment dispersion, and inkjet ink

ABSTRACT

There is provided a technique for producing a quinacridone solid solution pigment, the technique making it possible to obtain a quinacridone solid solution pigment which produces a colored product having high chroma and a bluish hue, more preferably which has controlled particle diameters. Specifically, a method for producing a quinacridone solid solution pigment, the method including a crude quinacridone solid solution production step of subjecting a diarylaminoterepththalic acid and a dialkylarylaminoterephthalic acid to a co-cyclization reaction in polyphosphoric acid, thereby obtaining a water-containing crude quinacridone solid solution containing a solid solution of an unsubstituted quinacridone and a 2,9-dialkylquinacridone, the solid solution containing water, a drying step of drying the water-containing crude quinacridone solid solution to reduce the water content to less than 1% and obtain a powdery, crude quinacridone solid solution, and a pigmentation step of heating the powdery, crude quinacridone solid solution in a liquid medium that cannot dissolve the crude quinacridone solid solution.

TECHNICAL FIELD

The present invention relates to a method for producing a quinacridonesolid solution pigment, a pigment dispersion liquid, and an inkjet ink.In detail, the present invention relates to: a method for producing aquinacridone solid solution, the method making it possible to obtain aquinacridone solid solution pigment which produces a colored producthaving high chroma and a bluish hue, the colored product obtained byapplying the method, more preferably which has controlled particlediameters in such an extent that the quinacridone solid solution pigmentcan be applied to an inkjet ink; a pigment dispersion liquid and aninkjet ink each containing a particular quinacridone solid solutionpigment that can be obtained by the production method.

BACKGROUND ART

A lot of studies on a quinacridone solid solution pigment have beenconducted in an organic pigment field, and, for example, a quinacridonepigment composed of a solid solution of an unsubstituted quinacridoneand 2,9-dimethylquinacridone, C.I. Pigment Red 206 which is aquinacridone pigment composed of an unsubstituted quinacridone and aquinacridone quinone, C.I. Pigment Red 207 which is a quinacridonepigment composed of a solid solution of an unsubstituted quinacridoneand 4,11-dichloroquinacridone, etc. are known (see Patent Literatures 1and 2).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2000-281930

Patent Literature 2: Japanese Patent Laid-Open No. 2002-146224

SUMMARY OF INVENTION Technical Problem

However, there has been a problem that the chroma of colored productsobtained from conventional quinacridone solid solution pigments is stillinsufficient. In addition, a quinacridone solid solution having a bluishhue has been desired in the market in recent years, but a quinacridonesolid solution which can fully satisfy this need in the market, thequinacridone solid solution having high chroma and a bluish hue, has notexisted yet. In addition, for example, a pigment for use as a colorantin an inkjet ink is required to be fine and have uniform particlediameters; however, there is a problem that it is difficult to controlthe size of the diameter of fine particles in solid solution pigments.

Accordingly, an object of the present invention is to provide atechnique by which a quinacridone solid solution pigment which forms acolored product having high chroma and a bluish hue, and, morepreferably, a quinacridone solid solution pigment having controlledparticle diameters and having desired particle diameters can beproduced. In addition, another object of the present invention is toprovide a pigment dispersion liquid and an inkjet ink each enablingformation of a colored product having high chroma and a bluish hue bydeveloping a technique that can provide an excellent quinacridone solidsolution pigment, as described above, which is suitable, for example, asa colorant for an inkjet ink.

Solution to Problem

The above-described problems of the conventional techniques are solvedby the present invention described below. That is, the present inventionprovides

[1] A method for producing a quinacridone solid solution pigment, themethod including: a crude quinacridone solid solution production step; adrying step of drying the crude quinacridone solid solution; and apigmentation step of heating the dried crude quinacridone solid solutionin a solvent, thereby making the dried crude quinacridone solid solutioninto a pigment, wherein: in the crude quinacridone solid solutionproduction step, a diarylaminoterephthalic acid and adialkylarylaminoterephthalic acid are subjected to a co-cyclizationreaction in polyphosphoric acid to obtain a water-containing crudequinacridone solid solution containing a solid solution of anunsubstituted quinacridone and a 2,9-dialkylquinacridone, the solidsolution containing water; in the drying step, the water-containingcrude quinacridone solid solution obtained in the solid solutionproduction step is dried to reduce a water content to less than 1% andobtain a powdery, crude quinacridone solid solution; and in thepigmentation step, the powdery, crude quinacridone solid solution isheated in a liquid medium that cannot dissolve the crude quinacridonesolid solution.

Preferred embodiments of the above-described method for producing aquinacridone solid solution pigment according to the present inventioninclude the following embodiments.

[2] The method for producing a quinacridone solid solution pigmentaccording to [1], wherein the diarylaminoterephthalic acid is2,5-dianilinoterephthalic acid, and the dialkylarylaminoterephthalicacid is 2,5-di(p-toluidino) terephthalic acid.[3] The method for producing a quinacridone solid solution pigmentaccording to [1] or [2], wherein a mass ratio of the unsubstitutedquinacridone to the 2,9-dialkylquinacridone is 20:80 to 40:60.[4] The method for producing a quinacridone solid solution pigmentaccording to any one of [1] to [3], wherein in the pigmentation step, aquinacridone-based pigment derivative is allowed to exist in heating thepowdery, crude quinacridone solid solution in the liquid medium.[5] The method for producing a quinacridone solid solution pigmentaccording to [4], wherein the quinacridone-based pigment derivative is2-phthalimidemethylquinacridone.[6] The method for producing a quinacridone solid solution pigmentaccording to any one of [1] to [5], wherein the liquid medium thatcannot dissolve the crude quinacridone solid solution is dimethylsulfoxide or 1,3-dimethyl-2-imidazolidinone.[7] The method for producing a quinacridone solid solution pigmentaccording to [6], wherein a heating temperature in the pigmentation stepis 60° C. or higher and 120° C. or lower.[8] The method for producing a quinacridone solid solution pigmentaccording to any one of [1] to [7], wherein the method is for obtaininga quinacridone solid solution pigment having major axis diameters ofparticles of 30 to 100 nm.

The present invention provides as other embodiments a pigment dispersionliquid and an inkjet ink described below.

[9] A pigment dispersion liquid containing: a quinacridone solidsolution pigment of an unsubstituted quinacridone and a2,9-dialkylquinacridone; a pigment dispersant; and water, wherein thequinacridone solid solution pigment has peaks at Bragg angles (2θ±0.2°)of 27.3°, 13.9°, and 5.6° in powder X-ray diffraction.[10] An inkjet ink containing: a quinacridone solid solution pigmentcomprising a solid solution of an unsubstituted quinacridone and a2,9-dialkylquinacridone, having major axis diameters of particles of 30to 100 nm; a pigment dispersant; and water, wherein the quinacridonesolid solution pigment has peaks at Bragg angles (2θ±0.2°) of 27 0.3°,13.9°, and 5.6° in powder X-ray diffraction.

Advantageous Effects of Invention

According to the present invention, a quinacridone solid solutionpigment which produces a colored product having high chroma and a bluishhue is provided, and it becomes possible to provide a quinacridone solidsolution pigment the particle diameters of which are controlled intoappropriate sizes, which further becomes an important effect in additionto the above-described effect in practical use. In addition, accordingto the present invention, it becomes possible to provide a pigmentdispersion liquid and an inkjet ink which can provide a colored producthaving high chroma and a bluish hue by applying the above-describedexcellent quinacridone solid solution pigment.

DESCRIPTION OF EMBODIMENTS

Next, the present invention will be described in more detail givingpreferred embodiments for carrying out the present invention. Thepresent inventors have conducted diligent studies in order to solve thepreviously described problems in the conventional techniques and havereached the present invention. That is, in a conventional method forproducing a quinacridone solid solution pigment, adiarylaminoterephthalic acid and a dialkylarylaminoterephthalic acid aresubjected to a co-cyclization reaction in polyphosphoric acid to producea water-containing crude quinacridone solid solution containing anunsubstituted quinacridone and a 2,9-dialkylquinacridone, and theobtained crude quinacridone solid solution is then heated in a solventkeeping the water-containing state to be made into a pigment, but on theother hand, the present inventors have completed the present inventionby finding that by newly providing, prior to the pigmentation step, adrying step of reducing the water content to less than 1% to make apowdery, crude quinacridone solid solution, a colored product formedwith the obtained quinacridone solid solution pigment has higher chromaand a bluisher hue than colored products obtained by using conventionalsolid solution pigments. In addition, according to the production methodof the present invention, it becomes possible to control the particlediameters of the quinacridone solid solution pigment to be obtained todesired sizes, and particularly, it becomes possible to obtain aquinacridone solid solution pigment having particle diameters suitablefor an inkjet ink for which the ejection stability of the ink isdesired.

<Method for Producing Quinacridone Solid Solution Pigment>

A method for producing a quinacridone solid solution pigment accordingto the present invention is characterized in that the method includes: acrude quinacridone solid solution production step; a drying step ofdrying the crude quinacridone solid solution; and a pigmentation step ofheating a dried, powdery, crude quinacridone solid solution in asolvent, thereby making the dried, powdery, crude quinacridone solidsolution into a pigment, and particularly, the drying step of drying awater-containing crude quinacridone solid solution is newly provided.Specifically, the method for producing a quinacridone solid solutionpigment is characterized in that in the crude quinacridone solidsolution production step, a water-containing crude quinacridone solidsolution is obtained in the same manner as in conventional methods forproducing a crude quinacridone solid solution, the water-containingcrude quinacridone solid solution obtained above is dried in the nextdrying step to reduce the water content to less than 1% and obtain apowdery, crude quinacridone solid solution, and the obtained powdery,crude quinacridone solid solution is thereafter heated in a liquidmedium that cannot dissolve the crude quinacridone solid solution,thereby making the obtained powdery, crude quinacridone solid solutioninto a pigment.

Further, according to studies conducted by the present inventors, byusing dimethyl sulfoxide or 1,3-dimethyl-2-imidazolidione as a liquidmedium in making a pigment, it becomes possible to control the particlediameters of the quinacridone solid solution pigment to be obtained toappropriate sizes. Particularly, when the heating temperature is set soas to fall within a range of 60° C. or higher and 120° C. or lower inmaking a pigment by performing heating in these liquid media, it becomesthereby possible to control the particle diameters of the quinacridonesolid solution pigment to be obtained stably to sizes suitable for theuse.

In addition, according to studies conducted by the present inventors,when a quinacridone-based pigment derivative is allowed to exist inmaking a pigment by heating the powdery, crude quinacridone solidsolution in the liquid medium, an effect of making the particles of thequinacridone solid solution pigment uniform and an effect of making thechroma of a colored product high can be thereby further enhanced.

The “quinacridone solid solution pigment” herein refers to a pigment inwhich a plurality of different quinacridone pigment molecules exist in amixed state of being dissolved in one another and in a uniform solidphase state, and does not mean a mixture obtained by simply mixing aplurality of different quinacridone pigments. It is known that theproperties such as color are changed by producing a solid solution. Thepresent invention intends to produce a solid solution of anunsubstituted quinacridone and a 2,9-dialkylquinacridone, and as asingle pigment, the unsubstituted quinacridone corresponds to C.I.Pigment Violet 19, and the 2,9-dialkylquinacridone corresponds to C. I.Pigment Red 122. Hereinafter, each step in the production methodaccording to the present invention will be described.

(Crude Quinacridone Solid Solution Production Step)

In the production method according to the present invention, adiarylaminoterephthalic acid and a dialkylarylaminoterephthalic acid arefirst subjected to a co-cyclization reaction in polyphosphoric acid toobtain a water-containing crude quinacridone solid solution containingan unsubstituted quinacridone, a 2,9-dialkylquinacridone, and water.Through the above-described co-cyclization reaction of thediarylaminoterephthalic acid and the dialkylarylaminoterephthalic acid,the water-containing crude quinacridone solid solution containing wateris obtained. This step is the same as a conventional method forobtaining a quinacridone-based solid solution pigment. In theconventional production method, the crude quinacridone solid solution ismade into a pigment keeping this water-containing state.

As the diarylaminoterephthalic acid for use in the above-described step,for example, 2,5-dianilinoterephthalic acid is preferable. In addition,as the dialkylarylaminoterephthalic acid, for example,2,5-di(p-toluidino) terephthalic acid is preferable. To more stablyobtain the quinacridone solid solution pigment which is the final objectin the present invention and which produces a colored product havinghigh chroma and a bluish hue, it is preferable to use these compounds.

According to studies conducted by the present inventors, to obtain thequinacridone solid solution pigment which is demanded in the market andwhich produces a colored product having high chroma and a bluish hue, itis preferable to perform design in such a way that the mass ratio of theunsubstituted quinacridone to the 2,9-dialkylquinacridone, which areobtained by the above-described co-cyclization reaction, is 20:80 to40:60.

(Drying Step)

The production method according to the present invention is differentfrom the conventional methods for producing a quinacridone solidsolution pigment, and it is required in the drying step, which is newlyprovided, that the water-containing crude quinacridone solid solutionobtained in the crude quinacridone solid solution production step bedried to obtain a powdery, crude quinacridone solid solution having awater content of less than 1%, and thereafter the powdery, crudequinacridone solid solution be made into a pigment. According to studiesconducted by the present inventors, by providing the drying stepspecified in the present invention, it becomes possible to obtain thequinacridone solid solution pigment which produces a colored producthaving high chroma and a bluish hue. That is, an important thing in thepresent invention is that the water-containing crude quinacridone solidsolution is dried sufficiently to be made into a powdery, crudequinacridone solid solution having a water content of less than 1%, andthe powdery, crude quinacridone solid solution is thereafter made into apigment. The technical characteristic of the present invention is inthat stably obtaining the quinacridone solid solution pigment with whicha colored product having high chroma and a bluish hue is obtained isrealized by newly providing the above-described drying step.

In contrast, even if the water-containing crude quinacridone solidsolution is dried, unless the water-containing crude quinacridone solidsolution is dried completely, specifically when the water content is 1%or larger, the hue of a colored product formed with a finally obtainedquinacridone solid solution pigment becomes yellowish, and therefore acolored product that satisfies the bluish hue which has been required inthe market in recent years is not obtained.

(Pigmentation Step)

In the production method according to the present invention, thepowdery, crude quinacridone solid solution obtained in the previouslydescribed drying step is heated in a liquid medium that cannot dissolvethe crude quinacridone solid solution in the subsequent pigmentationstep to obtain a quinacridone solid solution pigment. Basically, thepigmentation step may be the same as a pigmentation method performed inthe conventional methods.

Examples of the liquid medium that cannot dissolve the crudequinacridone solid solution for use in making a pigment includedimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, ethanol,propanol, butanol, and ethylene glycol. It is described in PatentLiterature 2 given previously as a conventional technique thatdimethylformamide and butanol are preferable among the above-describedliquid media. In addition, it is also described that as the heatingtemperature, an arbitrary temperature from 25 to 140° C. can be adopted.

On the other hand, the present inventors have conducted diligent studieson this pigmentation step to find that the particle diameters of thequinacridone solid solution pigment to be obtained are controlled toappropriate sizes corresponding to the use by devising the type of theliquid medium to be used as described previously and further, bydevising the temperature at which heating is performed in the liquidmedium.

Specifically, the present inventors have found that the particlediameters of the quinacridone solid solution pigment to be obtained canbe controlled into appropriate sizes by heating the powder of the crudequinacridone solid solution in a solvent of dimethyl sulfoxide or1,3-dimethyl-2-imidazolidinone in the pigmentation step performed afterobtaining the powdery, crude quinacridone solid solution having a watercontent of less than 1% in the drying step of drying thewater-containing crude quinacridone solid solution, the drying stepnewly provided in the production method according to the presentinvention. The present inventors have further found that by setting theheating temperature on that occasion to within a particular temperaturerange of 60° C. or higher and 120° C. or lower, the particle diametersof the quinacridone solid solution pigment to be obtained can be morestably controlled to the sizes suitable for the use. For example, in thecase where the quinacridone solid solution pigment for use in an inkjetink is obtained, when the heating temperature exceeds 120° C., theparticle diameters of the quinacridone solid solution pigment become toolarge, and on the other hand, when the heating temperature is lower than60° C., the particle diameters of the quinacridone solid solutionpigment become too small, and therefore it becomes difficult to dispersethe quinacridone solid solution pigment favorably in an aqueous medium.

According to studies conducted by the present inventors, theabove-described effect is particularly remarkable in the case wheredimethyl sulfoxide or 1,3-dimethyl-2-imidazolidinone is used as thesolvent for use in the pigmentation step, and, for example, a similareffect cannot be obtained with alcohol-based solvents, such as butanol,which are described as preferable in Patent Literature 2 givenpreviously as a conventional technique.

In addition, according to studies conducted by the present inventors,when a quinacridone-based pigment derivative is added and a pigment ismade in a state where the quinacridone-based pigment derivative isallowed to exist in heating the powdery, crude quinacridone solidsolution in dimethyl sulfoxide or 1,3-dimethyl-2-imidazolidinone, aneffect of making the particles of the quinacridone solid solutionpigment to be obtained and an effect of making the chroma of thequinacridone solid solution pigment to be obtained high are therebyfurther enhanced. As the quinacridone-based pigment derivative for useon this occasion, 2-phthalimidemethylquinacridone is preferable.

<Quinacridone Solid Solution Pigment>

As described previously, the quinacridone solid solution pigmentobtained by the method according to the present invention contains anunsubstituted quinacridone and a 2,9-dialkylquinacridone as essentialcomponents and forms a mixed phase in which the 2,9-dialkylquinacridoneis regarded as dissolving into a crystal phase of the unsubstitutedquinacridone. Therefore, the quinacridone solid solution pigmentobtained by the method according to the present invention has peaks atparticular Bragg angles by powder X-ray diffraction, the peaks notexisting in an unsubstituted quinacridone single crystal and a2,9-dialkylquinacridone single crystal. Accordingly, the solid solutionor the mixture of respective single crystals can be easily decided bythe powder X-ray diffraction.

The quinacridone solid solution pigment which is obtained by theproduction method according to the present invention and which canprovide a colored product having high chroma and a bluish hue ischaracterized by having peaks at Bragg angles (2θ±0.2°) of 27.3°, 13.9°,and 5.6° in the powder X-ray diffraction. In addition, the relativeintensity ratios of the peaks are about 60 to about 70 for the peak at13.9° and about 70 to about 80 for the peak at 27.3° when the intensityof the peak at 5.6° is assumed to be 100.

The particle diameters of the quinacridone solid solution pigmentobtained by the production method according to the present invention arenot particularly limited. As the quinacridone solid solution pigment foruse in an inkjet ink according to the present invention, the major axisdiameters of particles are required to be 30 to 100 nm when the ejectionstability of the inkjet ink is taken into consideration, and further, itis preferable that the major axis diameters of particles be about 50 nm.

<Inkjet Ink>

An inkjet ink according to the present invention contains a quinacridonesolid solution pigment having major axis diameters of particles of 30 to100 nm, the quinacridone solid solution pigment obtained by theproduction method according to the present invention describedpreviously. Further, the inkjet ink according to the present inventionis required to contain a pigment dispersant in order to improve thedispersibility and dispersion stability of the quinacridone solidsolution pigment and the storage stability of the ink with time. As thepigment dispersant, those which have been used in conventionally knownaqueous inkjet pigment inks can be appropriately used. Besides, ifnecessary, additives such as a surfactant, an organic solvent, and ahumectant may be added to the inkjet ink according to the presentinvention, and known techniques on aqueous inkjet pigment inks can alsobe applied to these additives.

The inkjet ink according to the present invention is characterized bycontaining a quinacridone solid solution pigment which is obtained bythe production method according to the present invention and whichproduces a colored product having high chroma and a bluish hue; however,the amount of addition of the quinacridone solid solution pigment is notparticularly limited and may be added in a conventionally known range.Specifically, the amount of addition of the quinacridone solid solutionpigment is 0.5 to 30% by mass and preferably about 4 to about 10% bymass in 100% by mass of the ink. When the amount of addition is lessthan 0.5% by mass, the print density cannot be secured in some cases,and on the other hand, when the amount of addition exceeds 30% by mass,a viscosity increase occurs in the ink and structural viscosity occursin viscosity properties, so that the ejection stability of the ink froman inkjet head may be deteriorated in some cases.

EXAMPLES

Hereinafter, the present invention will be further described givingExamples and Comparative Examples. It is to be noted that “%” and“parts” described below are each on a mass basis unless otherwisenoticed.

Example 1

Into a 100-ml separable flask, 65.6 g of 85% phosphoric acid was weighedand placed, and 9.87 g of phosphoric anhydride was added to prepare84.0% polyphosphoric acid. When the internal temperature was lowered toabout 100° C., 14.28 g of 2,5-di(p-toluidino) terephthalic acid(DM-DATA) and, subsequently, 6.12 g of 2,5-dianilinoterephthalic acid(DATA) were added gradually. After the addition was completed, acondensation reaction was performed at 120° C. for 4 hours. After thereaction was completed, the reaction liquid was put into a 1-L beakerwith 400 ml of normal temperature water filled therein. After filtrationand washing with water were performed, the resultant liquid wastransferred to a 1-L beaker, 800 ml of water was added, a resultantmixture was stirred, and caustic soda was added to adjust the pH to 7 to8. A resultant mixture was subjected to filtration and washing with hotwater to obtain a water-containing crude quinacridone solid solution.

The water-containing crude quinacridone solid solution obtained abovewas dried at 80° C. overnight to reduce the water content to less than1%. After the drying was completed, the quinacridone solid solution waspulverized to obtain 18.0 g of a powder of the crude quinacridone solidsolution. The obtained powder was observed with a transmission electronmicroscope to find that the average major axis diameter of particles wasabout 20 nm.

Next, dimethyl sulfoxide was used as a liquid medium that cannotdissolve the above-described powder to make the crude quinacridone solidsolution into a pigment. Specifically, 7.0 g of the powder of the crudequinacridone solid solution obtained above and 70.0 g of dimethylsulfoxide were loaded in a 100-mL separable flask, the temperature wasraised to 105° C. over 1 hour to perform a heating treatment at atemperature of 105° C. for 6 hours. After the treated mixture was cooledto 70° C. or lower, the treated mixture was subjected to filtration, andwashed with hot water and with water until the filtrate becamecolorless, and a residue was then dried at 80° C. to obtain a powder ofa quinacridone solid solution pigment of the present Example.

Whether the pigment obtained above is a quinacridone solid solutionwhich is an object of the present invention was checked by powder X-raydiffraction. Specifically, the powder of the quinacridone solid solutionpigment to be measured was filled in a predetermined holder, andmeasurement was conducted using miniFlex600 (trade name, manufactured byRigaku Corporation, the same apparatus was used in other examples),which is a powder X-ray diffraction apparatus. The results were suchthat the quinacridone solid solution pigment obtained above had peaks atBragg angles) (2θ±0.2°) of 27.3°, 13.9°, and 5.6° in the powder X-raydiffraction, and the intensity ratios of the peaks were such that theintensity of the peak at 13.9° was 65, and the intensity of the peak at27.3° was 75 when the intensity of the peak at 5.6° was assumed to be100.

In addition, the pigment particles of the quinacridone solid solutionpigment obtained above were observed with a transmission electronmicroscope to find that the average major axis diameter of the particleswas about 50 nm. This is denoted as a quinacridone solid solutionpigment 1. Evaluation results of the color of a colored product obtainedusing the quinacridone solid solution pigment 1 obtained above will bedescribed together with those of the other examples.

Example 2

In the present Example, the powdery, crude quinacridone solid solutionobtained in Example 1 was used and made into a pigment by being heatedfurther in the presence of a quinacridone-based pigment derivative.Specifically, 7.0 g of the powder of the crude quinacridone solidsolution obtained in Example 1, 70.0 g of dimethyl sulfoxide as a liquidmedium, and 0.35 g of a 2-phthalimidemethylquinacridone powder being aquinacridone-based pigment derivative were loaded in a 100-mL separableflask, and the temperature was raised to 105° C. over 1 hour to performa treatment at a temperature of 105° C. for 6 hours. After the treatedmixture was cooled to 70° C. or lower, the treated mixture was subjectedto filtration, and washed with hot water and with water until thefiltrate became colorless, and a residue was then dried at 80° C. toobtain a powder of a quinacridone solid solution pigment of the presentExample.

Whether the pigment obtained above is a quinacridone solid solutionwhich is an object of the present invention was checked by powder X-raydiffraction. Specifically, the pigment obtained above had peaks at Braggangles (2θ±0.2°) of 27.3°, 13.9°, and 5.6° in the powder X-raydiffraction, and the intensity ratios of the peaks were such that theintensity of the peak at 13.9° was 65, and the intensity of the peak at27.3° was 70 when the intensity of the peak at 5.6° was assumed to be100, and thus it was ascertained that the pigment obtained above is aquinacridone solid solution which is an object of the present invention.In addition, the pigment particles were observed with a transmissionelectron microscope in the same manner as in Example 1 to find that theaverage major axis diameter of the particles was about 40 nm. This isdenoted as a quinacridone solid solution pigment 2.

Example 3

In the present Example, the powdery, crude quinacridone solid solutionobtained in Example 1 was used and made into a pigment using a liquidmedium different from the liquid medium in Example 1. Specifically, 7.0g of the powder of the crude quinacridone solid solution obtained inExample 1, 70.0 g of 1,3-dimethyl-2-imidazolidinone as a liquid mediumwere loaded in a 100-mL separable flask, and the temperature was raisedto 105° C. over 1 hour to perform a treatment at a temperature of 105°C. for 6 hours. After the treated mixture was cooled to 70° C. or lower,the treated mixture was subjected to filtration, and washed with hotwater and with water until the filtrate became colorless, and a residuewas then dried at 80° C. to obtain a powder of a quinacridone solidsolution pigment of the present Example.

The pigment obtained above had peaks at Bragg angles (2θ±0.2°) of 27.3°,13.9°, and 5.6° in the powder X-ray diffraction, and the intensityratios of the peaks were such that the intensity of the peak at 13.9°was 65, and the intensity of the peak at 27.3° was 75 when the intensityof the peak at 5.6° was assumed to be 100, and thus it was ascertainedthat the pigment obtained above is a quinacridone solid solution whichis an object of the present invention.

In addition, the pigment particles were observed with a transmissionelectron microscope in the same manner as in Example 1 to find that theaverage major axis diameter of the particles was about 70 nm. This isdenoted as a quinacridone solid solution pigment 3. As describedpreviously, since the particle diameter of the quinacridone solidsolution pigment 1 was about 50 nm, the above-described results showthat the particle diameter of a solid solution pigment to be obtainedcan be changed by changing the type of the liquid medium for use inpigmentation.

Examples 4-1 to 4-5

In the present Examples, the powdery, crude quinacridone solid solutionobtained in Example 1 was used and made into pigments using dimethylsulfoxide as a liquid medium for use in pigmentation and changing theheating temperature of 105° C. to 50° C., 60° C., 80° C., 120° C., and130° C., and thus 5 types of quinacridone solid solution pigments wereobtained. As a result, as shown in Table 1, it was ascertained that theparticle diameter of a quinacridone solid solution pigment to beobtained changes according to the heating temperature. When this pointis utilized, a quinacridone solid solution pigment having a desiredparticle diameter according to the use thereof can be obtained. In Table1, the result of Example 1 where heating was performed at 105° C. isshown together.

TABLE 1 Difference in particle diameter among solid solutions obtainedin Examples 4-1 to 4-5 and Example 1 Exam- Exam- Exam- Exam- Exam- Exam-ple 4-1 ple 4-2 ple 4-3 ple 1 ple 4-4 ple 4-5 Heating 50 60 80 105 120130 temperature (° C.) Major axis about about about about about aboutdiameter of 20 30 40 50 100 120 particles (nm)

Examples 5-1 and 5-2

In the present Examples, quinacridone solid solution pigments were eachobtained using the powdery, crude quinacridone solid solution obtainedin Example 1 in the same manner as in Example 1 except that the liquidmedium for use in pigmentation was changed to each liquid medium shownin Table 2 in place of dimethyl sulfoxide used in Example 1. Theparticle diameters of the obtained quinacridone solid solution pigmentsare shown in Table 2. As a result, it was ascertained that the obtainedquinacridone solid solution pigments are unsuitable for the applicationto an inkjet ink because the particle diameters of the obtainedquinacridone solid solution pigments became smaller than in the case ofExample 1 as shown in Table 2.

TABLE 2 Difference in particle diameter among solid solutions obtainedin Examples 5-1 and 5-2 and Example 1 Example 5-1 Example 5-2 Example 1Type of liquid medium Iso- Diethylene Dimethyl butanol glycol sulfoxideMajor axis diameter about 20 about 25 about 50 of particles (nm)

Comparative Example 1

In the present Comparative Example, the water-containing crudequinacridone solid solution obtained in Example 1 was made into apigment as described below keeping the water-containing state withoutbeing dried and being made into a powder in the same manner as in theconventional techniques. In addition, methanol was used as the liquidmedium for use in pigmentation. Specifically, in a 300-mL containerwhich can be pressurized, 47.8 g (solid content: 7.0 g) of wet cakebeing a water-containing crude quinacridone solid solution and 95.2 g ofmethanol were loaded and stirred sufficiently, and a small amount ofcaustic soda was then added to adjust the pH to around 12. Subsequently,the temperature was raised to 105° C. over 0.5 hours, and heating andstirring were performed at a temperature of 105° C. for 6 hours. Theinternal pressure during the heating and stirring was 0.2 MPa at themaximum. The content was left standing to be cooled until thetemperature of the content reached room temperature, the content wasthen subjected to filtration and washed with hot water until thefiltrate became colorless, and a residue was then dried at 80° C. toobtain a quinacridone solid solution pigment of the present ComparativeExample.

Whether the pigment obtained above is a quinacridone solid solution waschecked by powder X-ray diffraction in the same manner as in Examples.Specifically, the obtained quinacridone solid solution pigment had peaksat Bragg angles (2θ±0.2°) of 27.3°, 13.9°, and 5.6° in the powder X-raydiffraction. However, the intensity ratios of the peaks were such thatthe intensity of the peak at 13.9° was 50, and the intensity of the peakat 27.3° was 56 when the intensity of the peak at 5.6° was assumed to be100, and therefore the intensity ratios of the peaks were different fromthose in Examples. In addition, the pigment particles were observed witha transmission electron microscope to find that the average major axisdiameter of the particles was about 140 nm. This is denoted as acomparative quinacridone solid solution pigment 1.

Comparative Example 2

The water-containing crude quinacridone solid solution obtained inExample 1 was made into a pigment keeping the water-containing statewithout being dried and being made into a powder in the same manner asin Comparative Example 1. In the present Comparative Example, dimethylsulfoxide was used in the same manner as in Example 1 as the liquidmedium for use in pigmentation. Specifically, in a 300-mL containerwhich can be pressurized, 47.8 g (solid content: 7.0 g) of wet cakebeing a water-containing crude quinacridone solid solution and 95.2 g ofdimethyl sulfoxide were loaded and stirred sufficiently. Subsequently,the temperature was raised to 130° C. over 0.5 hours, and heating andstirring were performed at a temperature of 130° C. for 6 hours. Theinternal pressure during the heating and stirring was 0.05 MPa at themaximum. The content was left standing to be cooled until thetemperature of the content reached room temperature, the content wasthen subjected to filtration and washed with hot water until thefiltrate became colorless, and a residue was then dried at 80° C. toobtain a quinacridone solid solution pigment of the present ComparativeExample.

Whether the pigment obtained above is a quinacridone solid solution waschecked by powder X-ray diffraction in the same manner as in Examples.The obtained quinacridone solid solution pigment had peaks at Braggangles (2θ±0.2°) of 27.3°, 13.9°, and 5.6° in the powder X-raydiffraction. However, the intensity ratios of the peaks were such thatthe intensity of the peak at 13.9° was 50, and the intensity of the peakat 27.3° was 54 when the intensity of the peak at 5.6° was assumed to be100, and therefore the intensity ratios of the peaks were different fromthose in Examples. In addition, the pigment particles were observed witha transmission electron microscope to find that the average major axisdiameter of the particles was about 200 nm. This is denoted as acomparative quinacridone solid solution pigment 2.

Comparative Example 3

A quinacridone solid solution pigment of the present Comparative Examplewas obtained in the same manner as in Comparative Example 1 except thata crude quinacridone solid solution having a water content of 5%, thecrude quinacridone solid solution obtained by drying thewater-containing crude quinacridone solid solution obtained in Example 1at 80° C. for 6 hours, was used. Whether the pigment obtained above is aquinacridone solid solution was checked by powder X-ray diffraction inthe same manner as in Examples. The obtained quinacridone solid solutionpigment had peaks at Bragg angles (2θ±0.2°) of 27.3°, 13.9°, and 5.6° inthe powder X-ray diffraction. However, the intensity ratios of the peakswere such that the intensity of the peak at 13.9° was 59, and theintensity of the peak at 27.3° was 68 when the intensity of the peak at5.6° was assumed to be 100, and therefore the intensity ratios of thepeaks were different from those in Examples. In addition, the pigmentparticles were observed with a transmission electron microscope to findthat the average major axis diameter of the particles was about 50 nm.This is denoted as a comparative quinacridone solid solution pigment 3.

<Evaluation>

An original color paint film and a light color paint film were eachprepared with a paint using the quinacridone solid solution pigmentobtained in each of Examples 1 to 3 and Comparative Examples 1 to 3, andL*a*b* values thereof were measured and evaluated. The results are shownin Table 3.

(Preparation of Paints)

1. Preparation of Base Paint

In a plastic container, 0.8 g of the pigment of each of Examples andComparative Examples, 5.0 g of an alkyd-melamine resin [106-3700 LacquerClear Art Clear (trade name); manufactured by Isamu Paint Co., Ltd.],5.0 g of a thinner [Nippe 2500 Thinner (trade name); manufactured byNIPPONPAINT Co., Ltd.], which contains toluene, ethyl acetate, andbutanol as the main components, and 50.0 g of a glass bead were loaded.This mixture was dispersed with a paint shaker for 1 hour, 35.0 g of theabove-described alkyd-melamine resin and 4.0 g of the above-describedthinner were then added, and a resultant mixture was dispersed for 10minutes. In a plastic container, 10.0 g of the dispersion liquid and20.0 g of the above-described alkyd-melamine resin were loaded, and aresultant mixture was dispersed and mixed with MAZERUSTAR to make a basepaint.

2. Preparation of Light Color Paint

In a plastic container, 0.8 g of the pigment of each of Examples andComparative Examples, 5.0 g of the previously described alkyd-melamineresin, 5.0 g of the previously described thinner, and 50 g of a glassbead were loaded. This mixture was dispersed with a paint shaker for 1hour, 35.0 g of the previously described alkyd-melamine resin and 4.0 gof the previously described thinner were added, and a resultant mixturewas dispersed for 10 minutes. In a plastic container, 10.0 g of thedispersion liquid thus obtained and 20.0 g of a white ink [10 Super 300White (trade name); manufactured by NIPPONPAINT Co., Ltd.], whichcontains titanium oxide as the main component, were loaded, and aresultant mixture was dispersed with MAZERUSTAR to make a light colorpaint.

3. Preparation of Colored Products and Evaluation of Hue (1) Each basepaint previously described was applied on white paper using a 6-milapplicator. This white paper was dried at room temperature for severalhours. Comparative evaluation of the hue was conducted by visualobservation and with a colorimeter with respect to each piece of coloredpaper (hereinafter, referred to as original color paint film) ofExamples and Comparative Examples thus prepared. The results are shownin Table 3. It is to be noted that the visual observation is relativeevaluation.

(2) Each light color paint was applied on white paper using a 6-milapplicator. This white paper was dried at room temperature for severalhours. Evaluation of the hue was also conducted with respect to eachcolored product (hereinafter, referred to as light color paint film)thus prepared in the same manner as described above.

The colorimetric values of Examples 1 to 3 and Comparative Examples 1 to3 are shown in Table 3. CM-3600d (trade name), which is aspectrophotometer manufactured by Konica Minolta, Inc., was used for thecolorimetric measurement. L* represents brightness and C* representschroma, and the chroma C* was determined by √(a*)²⁺+(b*)².

TABLE 3 Evaluation results Particle diameter of Visual pigment Cilluminant/ observation (nm) 10-degree field of view L* a* b* c* ShadeClarity Example 1 about 50 Original color paint film 42.63 70.42 −13.1471.64 Bluish High Light color paint film 60.86 45.11 −20.86 49.70 BluishHigh Example 2 about 40 Original color paint film 42.04 72.02 −13.4773.27 Bluish High Light color paint film 60.71 46.38 −20.67 50.78 BluishHigh Example 3 about 70 Original color paint film 42.91 70.56 −13.0971.76 Bluish High Light color paint film 60.74 45.46 −20.77 49.98 BluishHigh Comparative about 140 Original color paint film 43.68 70.84 −10.5871.63 Yellowish Low Example 1 Light color paint film 61.76 45.55 −18.3449.10 Yellowish Low Comparative about 200 Original color paint film42.73 69.06 −8.47 69.58 Slightly High Example 2 yellowish Light colorpaint film 61.55 44.60 −18.50 48.28 Slightly High yellowish Comparativeabout 50 Original color paint film 42.71 70.14 −12.40 71.23 SlightlyHigh Example3 bluish Light color paint film 60.98 45.04 −19.53 49.09Slightly High bluish

The difference between Example 1 and Comparative Example 2 is only inthat the drying step newly provided in the present invention does notexist in Comparative Example 2; however, as shown in Table 3, a largedifference was recognized in the b* value in particular. It is indicatedthat as the b* value becomes smaller, the hue becomes bluisher as aresult of a blue shift. It was ascertained that the solid solutionpigments obtained in the other Examples also had a smaller b* value anda bluisher hue than the evaluation samples each using the solid solutionpigment obtained in each Comparative Example which did not include thedrying step. In addition, when comparison is made between Examples andComparative Examples, the evaluation samples using the solid solutionpigments of Examples had larger values of the chroma C*. It wasascertained that the effect is particularly large in a system of Example2 where the quinacridone-based pigment derivative was used together inpigmentation. In addition, it was also ascertained the effect is largein the system of Example 2 in that the hue became bluish. It was alsoshown from the values of the chroma C* that the solid solution pigmentsof Examples have higher chroma C*, lower values of the brightness L*,and clearer hues than the solid solution pigments of ComparativeExamples. With respect to this point, the evaluation samples using thesolid solution pigments of Examples had higher clarity than theevaluation samples using the solid solution pigments of ComparativeExamples in the visual observation for light color paints.

[Inkjet Ink]

<Preparation of Magenta Color Aqueous Pigment Dispersion Liquid 1>

A pre-mill base was prepared by blending 200 parts of the quinacridonesolid solution pigment 1 obtained in Example 1 as a magenta pigment, 200parts of an aqueous solution (solid content of 30%) of anammonia-neutralized product of a styrene/2-ethylhexyl acrylate/acrylicacid (mass ratio of 50/30/20) copolymer (number average molecular weightof 7000 and acid value of 155 mgKOH/g) as a pigment dispersant, 30 partsof diethylene glycol monobutyl ether (hereinafter, abbreviated as BDG)as a liquid medium, and 340 parts of water, and deflocculating aresultant mixture with a disper. Subsequently, a dispersion treatmentwas performed on the obtained pre-mill base using a horizontal typemedia disperser “DYNO-MILL 0.6 Liter ECM TYPE” (trade name, manufacturedby Shinmaru Enterprises Corporation, zirconia bead diameter of 0.3 mm)at a peripheral speed of 7 m/s. The dispersion was completed at the timewhen the dispersion was performed for 1 hour to obtain a mill base.

The obtained mill base was diluted with ion-exchanged water so that thepigment content was 15%, and a centrifugal separation treatment wassubsequently performed to obtain a pigment dispersion liquid. Theobtained pigment dispersion liquid was subjected to filtration with a10-μm membrane filter, and ion-exchanged water, an antiseptic, andglycerin were added each in a predetermined amount to obtain a magentacolor pigment dispersion liquid 1 having a pigment concentration of12.1%.

The average particle diameter of the magenta color pigment dispersionliquid 1 obtained above was measured (25° C.) with a particle sizemeasuring instrument “NICOMP 380ZLS-S” (manufacture by Particle SizingSystems (PSS), LLC.) to find that the average particle diameter was 113nm. In addition, the viscosity was 3.58 mPa·s, the surface tension was44.9 mN/m, and the pH was 9.9. The formulation of the magenta colorpigment dispersion liquid 1 and the results of the physical propertiesare shown together in Table 4.

<Preparation of Magenta Color Aqueous Pigment Dispersion Liquid 2>

A magenta color aqueous pigment dispersion liquid 2 was obtained in thesame manner as the magenta color aqueous pigment dispersion liquid 1except that the comparative quinacridone solid solution pigment 1obtained in Comparative Example 1 was used in place of the quinacridonesolid solution pigment 1 used in the preparation of the magenta coloraqueous pigment dispersion liquid 1. The formulation of this pigmentdispersion liquid 2 and the results of the physical properties are showntogether in Table 4.

TABLE 4 Formulations and physical properties of magenta color pigmentdispersion liquids Aqueous pigment dispersion liquid 1 Aqueous pigmentdispersion liquid 2 Pre-mill base Pigment used Type Quinacridone solidsolution pigment 1 Comparative quinacridone solid (Pigment of Example 1)solution pigment 1 (Pigment of Comparative Example 1) Solvent for makingpigment Dimethyl sulfoxide Water/methanol Crystal structure CubicNeedle-like Amount of use 200 parts 200 parts Pigment dispersantStyrene/2-ethylhexyl acrylate/acrylic acid copolymer (mass ratio of50/30/20)*¹ Amount of dispersant 200 parts 200 parts BDG (in dispersant) 30 parts  30 parts Water 340 parts 340 parts Physical properties ofPigment content (%) 12.1 12.0 pigment dispersion liquid Average particlediameter(nm) 113 114 Viscosity (mPa · s) 3.58 3.77 Surface tension(mN/m) 44.9 44.4 pH 9.9 10.1 *¹Aqueous solution of ammonia-neutralizedproduct, number average molecular weight: 7000, acid value: 155 mgKOH/g,solid content of 30%

Next, the magenta color aqueous pigment dispersion liquid 1 obtainedabove was used, 5.0 parts of BDG, 2.5 parts of triethylene glycolmonobutyl ether (BTG), 18 parts of glycerin, 1 part of “SURFYNOL 465”(trade name, manufactured by Air Products and Chemicals, Inc.), andwater were added to 41.7 parts of the aqueous pigment dispersion liquid1 to adjust the total amount to 100 parts, and a resultant mixture wasstirred sufficiently. Thereafter, filtration was performed with amembrane filter having a pore size of 10 μm to obtain a magenta coloraqueous inkjet pigment ink 1.

The particle diameter of the pigment in the obtained ink was 113 nm, theviscosity of the ink was 3.53 mPa·s, and the pH was 9.7.

The previously prepared magenta color aqueous pigment dispersion liquid2 obtained using the comparative quinacridone solid solution pigment 1was used, and a magenta color aqueous inkjet pigment ink 2 containingthe dispersion liquid was prepared by the same method. The particlediameter of the pigment in the obtained ink was 114 nm, the viscosity ofthe ink was 3.53 mPa·s, and the pH was 9.7.

<Evaluation of Pigment Dispersion Liquids and Inks>

(Evaluation of Dispersion Stability/Storage Stability)

The viscosity and particle diameter of the magenta color aqueous pigmentdispersion liquids 1 and 2 and the magenta color aqueous inkjet pigmentinks 1 and 3 which were prepared above were measured at the initialstate and after they were left to stand at 70° C. for 7 days tocalculate the rate of the change in the viscosity (%) and the rate ofthe change in the particle diameter, and thus the dispersionstability/storage stability of the inks were evaluated. It is to benoted that any of the rates of the changes was determined from thepercentage (%) of 1−(value after 7 days)/(initial value) and wasevaluated according to the following criteria. The obtained results areshown in Table 5.

[Evaluation Criteria]

(Change in Particle Diameter)

Excellent: rate of change is less than ±5%

Good: rate of change is ±5% or more and less than 10%

Fair: rate of change is ±10% or more and less than 15%

Poor: rate of change is ±15% or more

(Change in Viscosity)

Excellent: viscosity is low, and rate of change is less than ±10%

Good: viscosity is high, and rate of change is less than ±10%

Fair: viscosity is low, and rate of change is ±10% or more

Poor: viscosity is high, and rate of change is ±10% or more

TABLE 5-1 Evaluation results of dispersion stability/storage stabilityof aqueous pigment dispersion liquids Average particle diameter (nm)Viscosity (mPa · s) After Rate of After Rate of Initial 7 days changeEvaluation Initial 7 days change Evaluation Aqueous pigment dispersionliquid 1 113 112 −0.9% Excellent 3.58 3.48 −2.7% Excellent (Pigment ofExample 1) Aqueous pigment dispersion liquid 2 114 114 0.0% Excellent3.77 3.65 −3.3% Excellent (Pigment of Comparative Example 1)

TABLE 5-2 Evaluation results of dispersion stability/storage stabilityof inkjet inks Average particle diameter (nm) Viscosity (mPa · s) AfterRate of After Rate of Initial 7 days change Evaluation Initial 7 dayschange Evaluation Aqueous pigment ink 1 113 114 0.9% Excellent 3.53 3.41−3.4% Excellent (Pigment of Example 1) Aqueous pigment ink 2 114 1162.0% Excellent 3.53 3.42 −3.1% Excellent (Pigment of Comparative Example1)

(Quality Evaluation of Printed Matter)

The magenta color aqueous inkjet pigment inks 1 and 2, which wereprepared above, were each filled in a cartridge and printed on 2 typesof paper, (i) dedicated photo glossy paper (PGPP) and (ii) plain paper(trade name “Xerox Business 4200 Paper”, manufactured by XeroxCorporation, US), using an inkjet printer (trade name “PM 4000PX”,manufactured by Seiko Epson Corporation.) with a photo mode to obtainprinted matter. As a result, it was ascertained that any of the aqueouspigment inks can be ejected from inkjet nozzles without a problem.

The quality of the obtained printed matter was evaluated using aspectrophotometer (trade name “i1 Basic Pro”, manufacture by X-RiteInc.). Specifically, the chroma C* and the optical density (OD value)were measured under the following conditions and evaluated for theobtained printed matter with the spectrophotometer. The measurementresults are shown in Table 6. In addition, the results of visualobservation of the shade are shown together. It is to be noted that withrespect to the optical density (OD value) and the chroma C*, a largervalue can be rated as more excellent.

[Measurement Conditions]

Optical density (ODvalue) on plain paper: average value of 6 points eachmeasured 3 times

Optical property (chroma C*) on plain paper: average value of 6 pointseach measured once

Optical density (OD value) on dedicated photo glossy paper: averagevalue of 3 points each measured once

Optical property (chroma C*) on dedicated photo glossy paper: averagevalue of 3 points each measured once

TABLE 6 Evaluation results of quality of printed matter Particlediameter Optical properties of printed matter of pigment in ink Plainpaper Glossy paper (nm) Chroma C* Shade OD value Chroma C* Shade ODvalue Aqueous pigment ink 1 113 59.5 Bluish 1.12 84.1 Bluish 2.12Aqueous pigment ink 2 114 58.2 Yellowish 1.11 82.0 Yellowish 2.04

From the results shown in Table 6, the printed matter obtained byprinting with the magenta color aqueous inkjet pigment ink 1 to whichthe quinacridone solid solution pigment 1 of Example 1 was applied hadmore excellent color developability (OD value) and chroma (C*) in bothof the cases where the magenta color aqueous inkjet pigment ink 1 wasprinted on the plain paper and on the glossy paper than the printedmatter obtained by printing with the magenta color aqueous inkjetpigment ink 2 using the comparative quinacridone solid solution pigment1 of Comparative Example 1, which was obtained by a conventionalproduction method. In addition, as a result of visual observation ofthese pieces of printed matter, it was ascertained that the printedmatter obtained by printing with the aqueous pigment ink 1 clearly hasbluisher color than the printed matter obtained by printing with theaqueous pigment ink 2. From this fact, it was ascertained that theprinted matter obtained by applying the quinacridone solid solutionpigment obtained by the production method according to the presentinvention has more excellent chroma and color developability to keep theprinted density at a higher level than the conventional printed matterand has an inkjet property which gives an image having a bluish hue thatcan satisfy the demands in the market sufficiently.

1. A method for producing a quinacridone solid solution pigment, themethod comprising: a crude quinacridone solid solution production step;a drying step of drying the crude quinacridone solid solution; and apigmentation step of heating the dried crude quinacridone solid solutionin a solvent, thereby making the dried crude quinacridone solid solutioninto a pigment, wherein: in the crude quinacridone solid solutionproduction step, a diarylaminoterephthalic acid and adialkylarylaminoterephthalic acid are subjected to a co-cyclizationreaction in polyphosphoric acid to obtain a water-containing crudequinacridone solid solution comprising a solid solution of anunsubstituted quinacridone and a 2,9-dialkylquinacridone, the solidsolution containing water; in the drying step, the water-containingcrude quinacridone solid solution obtained in the solid solutionproduction step is dried to reduce a water content to less than 1% andobtain a powdery, crude quinacridone solid solution; and in thepigmentation step, the powdery, crude quinacridone solid solution isheated in a liquid medium that cannot dissolve the crude quinacridonesolid solution.
 2. The method for producing a quinacridone solidsolution pigment according to claim 1, wherein thediarylaminoterephthalic acid is 2,5-dianilinoterephthalic acid, and thedialkylarylaminoterephthalic acid is 2,5-di(p-toluidino)terephthalicacid.
 3. The method for producing a quinacridone solid solution pigmentaccording to claim 1, wherein a mass ratio of the unsubstitutedquinacridone to the 2,9-dialkylquinacridone is 20:80 to 40:60.
 4. Themethod for producing a quinacridone solid solution pigment according toclaim 1, wherein in the pigmentation step, a quinacridone-based pigmentderivative is allowed to exist in heating the powdery, crudequinacridone solid solution in the liquid medium.
 5. The method forproducing a quinacridone solid solution pigment according to claim 4,wherein the quinacridone-based pigment derivative is 2phthalimidemethylquinacridone.
 6. The method for producing aquinacridone solid solution pigment according to claim 1, wherein theliquid medium that cannot dissolve the crude quinacridone solid solutionis dimethyl sulfoxide or 1,3-dimethyl-2-imidazolidinone.
 7. The methodfor producing a quinacridone solid solution pigment according to claim6, wherein a heating temperature in the pigmentation step is 60° C. orhigher and 120° C. or lower.
 8. The method for producing a quinacridonesolid solution pigment according to claim 1, wherein the method is forobtaining a quinacridone solid solution pigment having major axisdiameters of particles of 30 to 100 nm.
 9. A pigment dispersion liquidcomprising: a quinacridone solid solution pigment of an unsubstitutedquinacridone and a 2,9-dialkylquinacridone; a pigment dispersant; andwater, wherein the quinacridone solid solution pigment has peaks atBragg angles (2θ±0.2°) of 27.3°, 13.9°, and 5.6° in powder X-raydiffraction.
 10. An inkjet ink comprising: a quinacridone solid solutionpigment comprising a solid solution of an unsubstituted quinacridone anda 2,9-dialkylquinacridone, having major axis diameters of particles of30 to 100 nm; a pigment dispersant; and water, wherein the quinacridonesolid solution pigment has peaks at Bragg angles (2θ±0.2°) of 27.3°,13.9°, and 5.6° in powder X-ray diffraction.